The present invention relates to the general field of turbine engine compressors, and in particular for an airplane turbojet or turboprop. The invention relates more particularly to a device enabling the variable pitch stator vanes of a compressor stage to be guided.
The high-pressure compressor of an aviation turbine engine comprises a plurality of variable pitch stator vane stages alternating with stages of rotor blades. The stator vanes serve to modify the flow characteristics of gas depending on the operating speeds of the turbine engine.
Each variable pitch stator vane has a control pivot at its tip and a guide pivot at its root, the control pivot passing through a stator shell (referred to as a casing) of the turbine engine and co-operating with a member for controlling the pitch angle of the vanes, with the guide pivot being pivotally movable in a bushing housed in a recess in an inner ring of the turbine engine. By acting on the control member, it is thus possible to modify the pitch angle of the blades in the stage in question. Reference may be made to Documents FR 2 556 410 and FR 2 723 614, which describe various configurations for guiding such variable pitch stator vanes.
The compressor casing is generally made as two half-shells in order to make it easier to put into place. In order to reduce the weight and increase the performance of the assembly as a whole, proposals have been made to make the shell as a single piece (360°). Unfortunately, when the compressor casing is a single piece in the tangential direction, it becomes considerably more complicated to put the various portions of the compressor into place. In particular, having recourse to a casing made of two half-shells enables the stator elements of the compressor to be put into place individually, which stator elements can then surround the elements of the rotor.
With a single-piece casing, it is necessary to assemble in alternation a rotor stage and then a stator stage. Unfortunately, in certain compressor configurations, the rotor stage situated downstream from the stator stage that is to be put into place cannot be moved downstream because of the slope of the casing. Thus, under such circumstances, the only way the stator vanes can be inserted in their housings is to move the inner ring as far as possible towards the rotor disk situated downstream. Unfortunately, this manipulation does not always make it possible to insert the stator vanes without damaging them.
Furthermore, in order to dimension the rotor line of the compressor, the shroud line of the compressor needs to be as close as possible to the flow passage for the gas stream passing therethrough. This has the consequence of reducing space beneath the passage, which makes it necessary to reduce the radial size of the guide device for the stator vanes.